Schizophrenia is the most common type of psychosis caused by an excessive neurotransmission activity of the dopaminergic nervous system in the central nervous system. [Cf. "Hypothesis of Excessive Dopamine" by Michio Tohru: TAISHA (Metabol:sm), Vol. 22, pp. 49, (1985); and Pharmacia Review, No. 10, "KOKORO-TO-KUSURI (Mind and Drugs)" edited by Pharmaceutical Society of Japan.]
Heretofore, a number of drugs, having the activity for blocking the neurotransmission of dopaminergic receptor in the central nervous system, have been developed, the example for said drugs are phenothiazine-type compounds such as Chlorpromazine; butyrophenone-type compounds such as Haloperidol; and benzamide-type compounds such as Sulpiride. These known drugs are now used widely for the purpose of improving so-called positive symptoms in the acute period of schizophrenia such as hallucinations, delusions and excitations and the like.
However, many of these drugs are considered as not effective for improving so-called the negative symptoms which are observed in the chronic period of schizophrenia such as apathy, emotional depression, hypopsychosis and the like. In addition to the above, these drugs give important side-effects such as akathisia, dystonia, Parkinsonism dyskinesia and late dyskinesia and the like, which are caused by blocking the neurotransmission of dopaminergic receptor in the striate body. Furthermore, other side-effects such as hyperprolactinemia and the like given by these drugs are become other problems. [Cf. G. M. Simpson, E. H. Pi, and J. J. Sramek, Jr.: Drugs, Vol. 21, pp. 138 (1981).]
Under these circumstances, development of drugs for treating schizophrenia having safety and clinically effectiveness have been eagerly expected.
The present inventors have made an extensive study for the purpose of developing drugs for treating schizophrenia, which would be not only effective for improving the negative symptoms, but also effective for improving the positive symptoms of schizophrenia, furthermore such drugs would have less side-effects as compared with those shown by drugs known in prior art. As the result, the present inventors have successfully found carbostyril derivatives having strong activity for blocking neurotransmission of dopaminergic receptor. As to the side-effects given by known drugs for treating schizophrenia are for example, in the case of phenothiazine-type drugs, the orthostatic hypotension and hypersedation on the basis of strong .alpha.-blocking activity; and in the case of drugs having strong activity for blocking neurotransmission of dopaminergic receptor, the side-effects are so-called extrapyramidal tract syndromes such as catalepsy, akathisia, dystonia and the like caused by the blocking neurotransmission of dopaminergic receptor in the atriate body.
Among carbostyril derivatives known in prior art, those disclosed in U.S. Pat. No. 4,734,416; Canadian Patent No. 1,117,110; British Patent No. 2,017,701; German Patent Nos. 2,911,108, 1,912,105 and 2,953,723; Japanese Patent Kokai (Laid-open) Nos. 54-130,587 (1979), 55-127,371, (1980) and 62-149,664 (1987) are having chemical structural formulas of upper conception of carbostyril derivatives of the present invention.
Furthermore, carbostyril derivatives disclosed in U.S. Pat. No. 4,234,585 and European Patent No. 226,441 have chemical structural formula similar to that of carbostyril derivatives of the present invention, but the pharmacological activities thereof are different from those of possessed by the carbostyril derivatives of the present invention.
In addition to the above, the carbostyril derivatives disclosed in U.S. Pat. No. 4,234,584 have chemical structural formula similar to that of carbostyril derivatives of the present invention and also have pharmacological activities similar to those of shown by carbostyril derivatives of the present invention.
Carbostyril derivatives disclosed in Australian Patent No. 50252/85, Japanese Patent Kokai (Laid-open) Nos. 58-43952 (1983), 56-49359 (1981), 56-49360 (1981) and 56-49361 (1981) have substituents different from those of the carbostyril derivatives of the present invention.